In their native state, alumina-rich and silica-rich ceramic fiber materials are hydrophilic, adsorbing water onto their surface and permitting the interstices between fibers in a ceramic fiber insulation material to fill with water. If untreated, fibrous insulation materials can gain up to 600% of their weight in water. The ramifications of this hydrophilicity are significant. Reusable space vehicles are covered on the outside with fibrous ceramic insulation materials for protection from the heat of reentering the Earth's atmosphere. Unless this insulation is treated to repel water it can become saturated due to rain exposure or condensation and add enough weight to compromise the mission of weight-critical launch vehicles. In commercial airplane operations, internal fibrous ceramic insulation absorbs moisture by condensation, causing problems ranging from water dripping from the insulation onto the passengers in the passenger cabin (the "rain-in-the-plane" problem), weight uptake, and corrosion caused by long-term water exposure and contact with wet insulation on the interior of aluminum-based airplane structures.
Effective waterproofing and re-waterproofing of the Thermal Protection System (TPS), located on the exterior of reusable launch vehicles such as the NASA Space Shuttle Orbiter, is critical to maintaining the integrity of the TPS. Our improved waterproofing and re-waterproofing of the TPS will minimize the time required to effectively waterproof the TPS. Conventional waterproofing processes can be time-consuming, costly, and often involve labor-intensive manual injection of high concentrations of toxic materials into the insulation. The Space Shuttle Orbiter TPS requires waterproofing and approximately 43% of that area requires re-waterproofing before the next space flight. Conventional waterproofing processes can also contaminate other systems on the vehicle with the waterproofing agent.
We have shown the feasibility of using dilute waterproofing agent formulations having an alcohol/water carrier system that can decrease application times by 50X, that minimizes compatibility and contamination issues, and that is safe and environmentally compliant. Our new spray-on dilute carrier process uses 50X less waterproofing agent and costs about 30X less than the conventional process. Feasibility research shows the system to be generally effective for different TPS materials. Similar improvements are expected on other vehicles and other blanket and tile-based insulation systems.